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Mohammed N. Sabir
Pharmacognosy II Lecture 1
Lecture outlines…
Definition & Introduction…
Classification…
Physicochemical properties…
Isolation from nature…
Examples and medicinal uses…
Overview…
2 03-Apr-17 Tannins & Flavonoids
Pharmacognosy II Lecture 1
TANNINS
Tannins are large phenolic non-nitrogenous biomolecules
having astringent properties.
Most are water-soluble, the multiple phenolic hydroxyls and carboxylic groups
are responsible for astringency and bitterness.
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They are broadly divided into two groups:
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1-The hydrolysable tannins, which are formed by the
esterification of sugars (e.g. glucose) with gallic acid.
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2-The non-hydrolysable tannins, (condensed tannins)
occur due to polymerization (condensation) reactions
between flavonoids.
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Pharmacognosy II Lecture 1
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Isolation
Both hydrolysable and condensed tannins are highly
soluble in water and alcohol but insoluble in organic
solvents such as ether, chloroform, and benzene.
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The general method for the extraction of tannic acid
from various galls is either with water-saturated ether,
or with mixture of water, alcohol, and ether.
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Acetone is added to the extraction procedure to inhibit
interaction between tannins and proteins or interfere
with the hydrogen bonding between them, thus
increasing the yield.
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After extraction, the aqueous and ethereal layers are
separately concentrated, dried, and subjected to
further isolation and purification by chromatography.
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The hydrolysable tannins are hydrolysed with bases to
simple acids and sugars.
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A key feature of tannins is their ability to bind to
proteins, and they have been used to tan leather, clarify
beer and as astringent preparations in pharmacy.
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Pharmacognosy II Lecture 1
They have a very wide distribution in plant kingdom
and may be produced by a plant as a feeding deterrent,
as their binding to proteins may reduce the dietary
value of the plant as a food.
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Some of these tannins are also plant pigments as
anthocyanidins.
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Pharmacognosy II Lecture 1
Some chemical tests for identification of tannins…
• Reaction with FeCl3.
• Goldbeater's skin test.
• Stiasny's method.
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Pharmacognosy II Lecture 1
Tannic acid is a mixture of gallic acid esters of glucose
and is obtained from nutgall, which is an abnormal
tissue growth of the tree Quercus infectoria (Fagaceae)
(ÁÁ�ÖÓd) as a response of larva inoculation of insects.
19 Andricus kollari مازوو
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Pharmacognosy II Lecture 1
The galls are harvested and extracted with solvents
(ether and water); the aqueous layer is collected and
evaporated to yield tannic acid, which is further
purified and used as a topical preparation for cold
sores.
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Epigallocatechin gallate (EGCG), epigallocatechin-3-
gallate, is the ester of epigallocatechin and gallic acid,
and is a type of catechin.
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EGCG is the most abundant catechin in tea and is a
potent antioxidant that have therapeutic applications in
(e.g. cancer). [It is found in green tea but not black tea].
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In black tea production, the catechins are converted to
theaflavins and thearubigins under high temperature,
an epimerization change is more likely to occur.
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Theaflavin derivatives in black tea and catechin derivatives in green tea inhibit HIV-1 entry by targeting gp41
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In addition to antioxidant and antiviral actions, tannins
also posses antimicrobial action.
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Tannin toxicity for fungi, bacteria and yeasts is due to
different mechanisms as been proposed include:-
Inhibition of extracellular microbial enzymes, deprivation of
the substrates required for microbial growth.
Direct action on microbial metabolism through inhibition of
oxidative phosphorylation.
Iron chelation is also proposed.
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Many microorganisms can overcome plant defenses
based on tannins through:-
Synthesis of tannin-complexing polymers.
Oxidation, tannin biodegradation.
Synthesis of siderophores.
See the reference… https://www.researchgate.net/publication/223084771_Antimicrobial_properties_of_tannin [accessed Apr 1, 2017].
Pharmacognosy II Lecture 1
The most important herbs rich with tannins used in
treatment of diarrhoea include:
- Sangisorba officinalis L.
- Acacia catechu Willd.
- Oak bark
- Quercus robur L.
- Potentilla erecta (L.) Rausch.
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Tannin-containing drugs are generally safe, but care
should be taken with concurrent administration of
other drugs since tannins are not compatible with
alkalis or alkaloids, and form complexes with proteins
and amino acids.
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Tannins in Herbal Medicine Punica garnatum (Lythraceae)
In the ancient Ayurveda system of medicine, the
pomegranate has extensively been used as a source of
traditional remedies for thousands of years.
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General uses of tannins
-Astringent (ppt. of Proteins).
-Hypolipidemic agents.
-Identification of Alkaloids.
-Tan leather.
-In Burns.
-Antidiarrheal agent.
-Antioxidant.
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Hamamelis Leaf (Witch hazel leaves)
Dried leaf of Hamamelis virginiana (Hamamelidaceae)
Hama = sametime
Melis = leaf
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Distilled witch hazel extract: prepared by steam
hydroalcoholic distillation of the dried leaves and twigs
of H. virginiana. Contains the volatile oil of the plant.
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Presence of tannins in fresh water
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Flavonoids and Flavonolignans
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•Introduction
-Are the largest group of naturally occurring phenolic compounds
-They occur in different plant parts (fruits, stem, barks, root, leaves, heartwood, flowers)
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Pharmacognosy II Lecture 1
•Introduction
-They are plant pigments or co-pigments (the yellow color of many fruits)
-They are found in different plant families (Rutaceae, Rosacea, Astraceae, Lamiaceae, Moraceae, Rubiaceae, and Myrtaceae)
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Pharmacognosy II Lecture 1
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The biosynthesis of flavonoids I- Phenyl propanoids (4-hydroxy coumaric acid) II- MalonylCoA
Pharmacognosy II Lecture 1
Role of flavonoids in plants
1. Insect attractant (pollinating agents)
2. Plant pigments
3. Growth regulators
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Pharmacognosy II Lecture 1
Role of flavonoids in medicine •Antioxidants (free radical scavengers)
•Antimicrobial
•Mitochondrial adhesion inhibitors
•Antiulcers
•Estrogen receptor binding
•Cell cycle arrest
•Topoisomerase inhibitors
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Pharmacognosy II Lecture 1
Examples… 1-Naringin From Citrus paradisi Fam: Rutaceae
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Studies have shown that naringin has a cholesterol-lowering effect, reduces LDL oxidation and can help to prevent hypercholesterolemia.
Naringin is an aldose reductase inhibitor which means
that it can help to fight diabetic retinopathy.
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Pharmacognosy II Lecture 1
Naringin (and grapefruit) drug interactions
-Interfere
1. Calcium channel blockers
2. Sedatives
3. Cholesterol lowering drugs
4. Caffeine
5. Estrogen
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Metabolic interaction through interfering metabolism of these drugs and increasing their t1/2.
Pharmacognosy II Lecture 1
Naringin enhance our perception of taste by
stimulating the taste buds; that's why some people
consume a small amount of grapefruit juice before a
meal.
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Pharmacognosy II Lecture 1
Citrus aurantifolia Peels Fam: Rutaceae
Uses:- Capillary bleeding (membrane stabilizer) 03-Apr-17 Tannins & Flavonoids 47
Pharmacognosy II Lecture 1
Flavonolignans
Silymarin (Silybum marianum L.) Milk Thistle Fam: Astraceae
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Hepatotoxic agents
•CCl4
•CHCl3
•Acetaminophen (Paracetamol©)
•Amanita phalloides
•Xenobiotics
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Fatty degeneration in Rat Liver after exposing to CCl4.
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Pharmacognostic Study of Silybum marianum, Mohammed Sabir, Lambert Academic Publishing, Germany, 1st Ed. 2014.
Pharmacognosy II Lecture 1
Mechanisms of action of Silybins
1. As antioxidant (inhibit lipid-peroxidation) through
free radical scavenging (antioxidant) Key
mechanism.
2. Regulators of intracellular content of glutathione.
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Pharmacognosy II Lecture 1
Mechanisms of action of Silybins 3. Cell membrane stabilizer and permeability
regulator that prevent entrance of toxins. 4. Promoters of ribosomal RNA synthesis and
stimulating liver regeneration (Hepatocytes protein synthesis).
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Mechanisms of action of Silybins 5. Inhibits transformation of stellate hepatocytes
into myofibroblasts.
6. Decrease the activity of tumor promoters.
7. Enhances apoptosis.
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Water solubility problems of silybin and methods of
enhancing its solubility…
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Water solubility affects bioavailability and its efficacy…
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JZS (2015) 17-3 (Part-A)
Bioavailability Enhancement of Silybin Through Carbon-23 Acid Derivatization Lena Nawzad Amin 1, Mohammed N. Sabir 2, Emad Manhal Al-Khafaji 3, Shwan Rachid 4
School of Pharmacy, Dept. of Pharmacognosy & Pharmaceutical Chemistry, Sulaimani University, Old campus, Sulaimaniyah Iraq Faculty of Science, Dept. of Chemistry University of Sulaimani, Qiliasan, Sulaimaniyah-Iraq Faculty of Sciences and Health, Koya University, Koya-Iraq.
Pharmacognosy II Lecture 1
Product Milk Thistle Herb Silybum marianum
Size - Mg. Silymarin Silybin Silymarin / Silybin
- Fruit referred to as seed one cap/tab Percent of product % in mg.
Maximum Milk Thistle (Siliphos) (Natural Wellness)
Dried extract (Siliphos)
240 mg.
33% 80 mg.
Thisilyn (Nature's Way)
Dried extract
175 mg. 80% 140 mg.
Legalon (Madaus, Germany)
Dried extract (40:1) 90 mg. 80%
70 mg.
Silymarin 80 (Planetary Formula)
Seed Extract plus Milk Thistle seed
210 mg. (plus 50 mg.)
80%
168 mg.
Milk Thistle (Kroeger)
Seed Extract plus Milk Thistle seed
175 mg. (plus 275 mg.)
80%
140 mg.
Silymarin (MediHerb, Australia)
Extract (70:1) 210 mg.
80% 168 mg.
Milk Thistle Seed (Gaia Herbs)
Liquid extract (1:1) 35 mg. 50%
17.5 mg.
Milk Thistle (generic) limited information
Extract 200 mg. 80%
160 mg.
Selected Milk Thistle Products
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NOTES : - Natural Wellness also has a product called UltraThistle that contains 360 mg
of silybin phytosome per capsule . - Thisilyn (distributed in the United States) uses the same ingredients as Legalon (Germany( - Silymarin 80 contains 50 mg of organically grown and processed milk thistle
seed. - Siliphos and Phytosome are registered trademarks of Indena (Italy.(
- Silybin Phytosome is also available from Enzymatic Therapy – 120 mg per
capsule.
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Lecture overview…
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Thanks for listening…
Any questions?
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Pharmacognosy II Lecture 1